The present invention relates to position computation apparatus and methods, more particularly, to apparatus and methods for position computation for a device located within the coverage area of a radio communication system.
Wireless (or radio) communication networks are commonly employed to provide voice and data communications to a plurality of subscribers within a prescribed geographic area. For example, analog cellular radiotelephone systems, such as those designated AMPS, ETACS, NMT-450, and NMT-900, have been deployed successfully throughout the world. Recently, digital cellular radiotelephone systems such as those designated IS-54B (and its successor IS-136) in North America and GSM in Europe have been introduced and are currently being deployed. These systems, and others, are described, for example, in the book entitled Cellular Radio Systems, by Balston, et al., published by Artech House, Norwood, Mass. (1993). In addition to the above systems, an evolving system referred to as Personal Communication Services (PCS) is being implemented. Examples of current PCS systems include those designated IS-95, PCS-1900, and PACS in North America, DCS-1800 and DECT in Europe, and PHS in Japan. These PCS systems operate at the 2 gigahertz (GHz) band of the radio spectrum, and are typically being used for voice and high bit-rate data communications.
Wireless systems, such as those identified above, may include one or more wireless mobile terminals that communicate with a plurality of cells served by base stations which are in turn connected to a Mobile Telephone Switching Office (MTSO). These base stations are typically placed in a fixed geographic location and cover a limited geographic region, generally referred to as a cell, located in the proximity of the base station.
The cells generally serve as nodes in the radio communication network, from which links are established between wireless mobile terminals by way of the base stations servicing the cells. Each cell will typically have allocated to it one or more dedicated control channels and one or more traffic channels. The control channel is a dedicated channel used for transmitting, typically by broadcasting, cell identification, paging and other information.
Other technologies rely on receipt of wireless transmissions to provide beneficial information. One such technology is the Global Positioning System (GPS). It will be understood that the terms xe2x80x9cglobal positioning systemxe2x80x9d or xe2x80x9cGPSxe2x80x9d are used to identify any spaced-based system that measures positions on earth, including the GLONASS satellite navigation system in Europe. As is well known to those having skill in the art, GPS is a space-based triangulation system using satellites and computers to measure positions anywhere on the earth. GPS was first developed by the United States Department of Defense as a navigational system. Compared to other land-based systems, GPS may be unlimited in its coverage, may provide continuous 24-hour coverage regardless of weather conditions, and may be highly accurate. While the GPS technology that provides the greatest level of accuracy has been retained by the government for military use, a less accurate service has been made available for civilian use.
In operation, a constellation of satellites orbiting the earth continually emit a GPS radio frequency signal at a predetermined chip frequency. A GPS receiver, e.g., a hand-held radio receiver with a GPS processor, receives the radio signals from the closest satellites and measures the time that the radio signals take to travel from the GPS satellites to the GPS receiver antenna. An example of such a receiver is the xe2x80x9cJupiterxe2x80x9d GPS receiver board available from Rockwell Semiconductor Systems which is described in a Data Sheet dated Jan. 19, 1998. By multiplying the travel time by the speed of light, the GPS receiver can calculate a range for each satellite in view. From additional information provided in the radio signal from the satellites, including the satellite""s orbit and velocity and correlation to its onboard clock, the GPS processor can calculate the position of the GPS receiver through a process of triangulation.
One problem with GPS systems is the time and power required to initially acquire a communication connection with a sufficient number of positioning satellites to compute a position. In particular, if the GPS detection system does not have any estimate of its location, it does not know which of the constellation of satellites is within view nor the location in space of the satellites in its viewing area. Accordingly, a cold start is required for acquisition which typically consumes a significant amount of power and requires more time than a warm start (i.e. a start with an initial position estimate). A typical GPS receiver, such as the Jupiter receiver from Rockwell Semiconductor Systems, has different satellite acquisition modes of operation. A first mode is warm start. This states typically occurs after a period of continuous operation or after a short idle period, wherein position, time, velocity and ephemeris data are reasonably valid. A warm start typically results in the shortest acquisition period. A second mode is initialized start wherein the user supplies position and time information, or information from a previous operation is available from onboard memory. Unlike warm start, as velocity and ephemeris data are not available in this mode, acquisition times are typically slower. A third mode is cold start in which the only information available may be almanac information to identify previously operational satellites. This mode accordingly provides slower acquisition than warm start or initialized start. Finally, the slowest acquisition time is provided by what is referred to as frozen start in which no information at all is available before seeking to acquire a satellite.
Another method previously used to improve the accuracy of a GPS system is differential GPS with broadcast corrections. In this approach, the normal transmission from a GPS satellite contain systematic errors which may be removed by using correction information broadcast by entities such as the Coast Guard. These broadcasting entities obtain correction information by comparing their known position to the position calculated using the GPS information received from the transmitting positioning satellite. This information is typically broadcast on specific subcarriers by the entities. Using this type of information, a GPS receiver can improve the accuracy of its calculation. However, while this method may be expected to improve the accuracy of the receiver, it does not provide improved acquisition time or reduce power consumption for the receiver.
It would be desirable to provide for warm start under as many conditions as possible. It is known to obtain position data from a user, for example, by keypad entry. It is also known to use previous position data that has been stored in memory. However, these approaches typically require user input and generally do not provide ephemeris data with which to reduce acquisition time and lower power consumption.
In light of the foregoing, it is an object of the present invention to provide apparatus and methods for position computation with warm start acquisition of a positioning satellite.
It is another object of the present invention to provide apparatus and methods for position computation with warm start which may be provided with minimal additional hardware and utilizing existing radio communication networks.
It is yet another object of the present invention to provide apparatus and methods for position computation with warm start which may be provided without requiring an account with existing radio communication networks.
These and other objects, features and advantages are provided according to the present invention by apparatus and methods for a position computation with high accuracy, low acquisition time and low power consumption. The position computation apparatus includes a radio communication receiver which monitors a radio communication network, such as a cellular network, covering the geographic region in which the position computation apparatus is located. The apparatus demodulates the signal from the radio communication network and obtains positioning data from the broadcast channel of the network for use in satellite acquisition operations prior to computing a position. The apparatus further includes a receiver for receiving positioning messages broadcast by a constellation of GPS satellites. A position computation circuit in the apparatus utilizes the positioning data obtained from the radio communication network in initial acquisition of one or more positioning satellites. Once the desired number of positioning satellites have been acquired, positioning messages are received from the acquired positioning satellites and used to calculate the position of the position computation apparatus.
By receiving position data from a base station of a radio communication network, as well as ephemeris data for positioning satellites in the viewing area of the base station/computation apparatus and timing information, the position computation apparatus of the present invention is able to generally operate in warm start mode for satellite acquisition at all times when access to the radio communication network is available, thereby providing for the lowest power consumption and fastest acquisition time for position computation operations.
The receiver for the radio communication network may be a simplified receiver as two way communications are not required and the receiver need only be able to synchronize with and demodulate and decode positioning data incorporated pursuant to a predetermined protocol in a broadcast control channel of the radio communication network. Preferably, the position computation apparatus need not even obtain an account with the radio communication network in order to monitor the positioning data transmitted by base stations over the air. However, if an account is required by the radio communication network provider, and encryption is provided to prevent unauthorized users from accessing the information, the benefits of the present invention may still be obtained by providing the appropriate decryption circuitry in the position computation apparatus.
In one aspect of the present invention, a mobile position computation apparatus for use within a region serviced by a radio communication network is provided. The apparatus includes a first receiver for receiving a radio communication broadcast over the radio communication network and a second receiver for receiving positioning messages broadcast by a positioning satellite. A position computation circuit is coupled to the second receiver. Finally, a means is provided coupled to the first receiver for obtaining positioning data from the radio communication broadcast and providing the positioning data to the position computation circuit for use in acquisition of the positioning satellite. The means for obtaining positioning data in one embodiment includes means for demodulating and decoding the radio communication, means for obtaining the positioning data from the demodulated and decoded radio communication and means for providing the position computation circuit the positioning data obtained from the demodulated and decoded radio communication.
The positioning satellite may be a global positioning system satellite. The radio communication network may be a cellular communication network. The radio communication is preferably broadcast over the radio communication network on a broadcast control channel.
In a further aspect of the present invention, the positioning data is selected from the group consisting of ephemeris data for the positioning satellite, position of a base station transmitting the radio communication, clock correction information and a framing structure timestamp for the broadcast control channel. The position computation circuit includes means for warm starting acquisition of the positioning satellite based on the positioning data. In one embodiment of the present invention, the position computation circuit further includes means for limiting the time window and the Doppler frequency range over which it searches for the positioning messages broadcast by the positioning satellite based on the positioning data. The position computation circuit may further include means for selecting a subset of a plurality of positioning satellites as the positioning satellite based on the positioning data.
In a further embodiment of the present invention, a method is for acquisition of a positioning satellite from within the coverage area of a radio communication network broadcasting positioning data. The positioning data is received over the radio communication network. A positioning satellite is acquired based on the received positioning data. In one embodiment of the method aspects of the present invention positioning messages are received from the acquired positioning satellite.